# Thread: what is the domain of this function

1. ## what is the domain of this function

can anyone help tell me what the domain of this function is please

f(x) = 1
_________

sqr root of (1-x)(7+x)

2. Originally Posted by emmalou264
can anyone help tell me what the domain of this function is please

f(x) = 1
_________

sqr root of (1-x)(7+x)
What makes f(x) undefined. ie What make the denominator 0, or what makes the radical undefined (negative)

The domain is all values of x for which the function is defined.

I'll give u one place that it's not defined.........

x<-7

here's another

x>1

here's another

x=1

here's another

x=-7

So are you familiar with interval notation?

$\displaystyle (-7,1)$

3. Originally Posted by VonNemo19
What makes f(x) undefined. ie What make the denominator 0, or what makes the radical undefined (negative)

The domain is all values of x for which the function is defined.

I'll give u one place that it's not defined.........

x<-7

here's another

x>1

here's another

x=1

here's another

x=-7

So are you familiar with interval notation?

$\displaystyle [-7,1]$
A square bracket means that the endpoint is included. A round bracket means that the endpoint is not included. So a slight correction to this answer is required: (-7, 1).

@OP: Since $\displaystyle (1 - x)(7 + x) > 0$ is required, the interval is most easily found by drawing a graph of the parabola $\displaystyle y = (1 - x)(7 + x)$ and looking for the values of x such that y > 0.

4. Originally Posted by mr fantastic
A square bracket means that the endpoint is included. A round bracket means that the endpoint is not included. So a slight correction to this answer is required: (-7, 1).

@OP: Since $\displaystyle (1 - x)(7 + x) > 0$ is required, the interval is most easily found by drawing a graph of the parabola $\displaystyle y = (1 - x)(7 + x)$ and looking for the values of x such that y > 0.
I simply cannot believe I did that. aaaaaaarrrrrrrrrrrrrrrrrgggggggggghhhhhhhhh!!!!!!! !!!!!!!